1. Field of the Invention
The present invention relates generally to apparatus and methods used in the completion of lateral wellbores and more particularly to new and improved apparatus and methods for ensuring adequate flow and production from lateral bores and still more particularly to apparatus and methods such as a tie-back insert for sealing around a window cut in a casing and extending a liner into a lateral borehole.
2. Description of the Related Art
It has become a common practice to drill deviated, and sometimes horizontal, lateral boreholes from a primary wellbore in order to increase production from a well. For example, the primary wellbore may be produced along with a lateral wellbore. Therefore, if production from the primary wellbore cannot be enhanced, the primary wellbore may be side tracked to produce the lateral borehole in order to produce another production zone in the well at the same time.
A whipstock and mill assembly is used to create a window in the wall of the casing of the primary wellhole. The lateral wellbore is then drilled through this window out into the formation where new production can be obtained.
Production from a lateral borehole can be difficult if the lateral borehole is drilled through a loose or unconsolidated formation. Formations that contain a significant amount of shale can be a particular problem. If the bore surfaces at and near the junction are not covered with a liner, chips and aggregate in this area tend to be drawn along with the produced fluids and foul the production. Unfortunately, lining the bore surfaces near the junction can be complex and time consuming.
There have been attempts to use a perforated insert through the window to allow production from both the primary bore and lateral bore while reducing contamination from chips and aggregate. The perforations are aligned with the primary bore and fluid from the primary bore passes through the perforations. Unfortunately, the perforations tend to become clogged by the chips and aggregate and allow the chips and aggregate to contaminate the product, thereby reducing the effectiveness of this type of insert.
The junction of the lateral borehole with the primary wellbore is usually ragged and rough as a result of the milling of the window through the casing to drill the lateral borehole. It is particularly difficult to seal around the window which is of a peculiar shape and has a jagged edge around its periphery.
A large area is exposed to the formations when the window is cut in the casing. A tie-back assembly may be disposed adjacent the junction of the lateral borehole and primary wellbore. See for example U.S. Pat. No. 5,680,901. The tieback assembly and liner limit the exposure of the formation through the window cut in the casing.
U.S. Pat. No. 5,875,847 discloses a multilateral sealing device comprising a casing tool having a lateral root premachined and plugged with cement. A profile receives a whipstock for the drilling of the lateral bore hole through the lateral root and cement plug. A lateral liner is then inserted and sealed within the lateral root.
The TAML (Technology Advancement Multi-Lateral) defines six levels for a multi-lateral junction for a lateral borehole. For example, if the liner is merely cemented at the junction, it is a level four since cement is not acceptable as a seal. Level five requires pressure integrity at the junction. Level six requires a hydraulic seal around the window for pressure integrity and full bore access to both the primary wellbore and the lateral borehole.
Various devices have been used to provide separate bores inside a primary wellbore. For example, in dual bore completions, a diverter sub has an initial single bore that is divided into two side by side bores, typically of equal diameter. A liner is hung in each of the two bores with a seal receptacle on top of the liner hanger. Additional equipment may be used with the diverter sub to cause one of the bores to communicate with a lateral borehole. The prior art scoop head or diverter or side-by-side bores include side-by-side conduits which extend axially and do not extend laterally into a lateral borehole. Further, these devices do not bridge the window cut in the casing.
One prior art device includes a large manifold that has a plurality of bores through it so that each of the bores can be used for different boreholes. The manifold includes one principal bore with three or four smaller bores, all beside each other shooting off from the main bore. The smaller bores are up to one-half the diameter of the main bore which severely reduces the size of pipe which can be used. Further the manifold is 12xc2xc inches in diameter and must be run on the bottom of the casing. This requires that a 12xc2xc inch borehole be drilled for a 9⅝ inch completion to allow the installation of 4xc2xd inch liners in the lateral borehole and in the main bore. The borehole beneath the manifold must be under-reamed. This prior art device is used in drilling and completing a new well.
Another prior art device is a level six system which includes an insert having two legs with one of the legs being compressed and the other leg being slightly compressed. The entire assembly is run into the primary wellbore and, once in position, the two legs are expanded to form two side-by-side bores. This is equivalent to a seven inch liner access and allows the drilling of a six or 6xc2xc inch hole. A 4xc2xd inch liner is then inserted into each of the bores. This system also has to be installed through a 12xc2xc inch hole and run in on the bottom of 9⅝ inch casing. Further, the legs have to be inflated once in position. To inflate the legs, the borehole must be bigger then a 12xc2xc inch borehole and thus the borehole must be under-reamed. This prior art device is used in drilling and completing a new well.
The present invention overcomes the deficiencies of the prior art.
The present invention features improved apparatus and methods for effectively obtaining production from a lateral borehole even where the formation is loose or unconsolidated. The invention includes a tie-back insert that is installed within the primary wellhole. The insert has a housing which includes one or more axial bores therethrough and a lateral bore which extends laterally out the side of the housing. The lateral bore allows a liner to extend from the top of the insert, through the lateral bore and into the lateral borehole to the new producing formation. The annulus formed between the housing and the casing is sealed at the upper end of the housing by an upper packer and the lower end of the housing is sealed by stabbing into a lower packer. The upper and lower packers seal around the window cut in the casing. The axial bores allow production fluid from the primary wellbore to be transmitted through the insert to the surface of the well. The insert is placed within the primary wellbore so that the lateral bore is located and oriented adjacent the lateral borehole allowing production fluid from the lateral borehole to be transmitted to the surface of the well.
Thus, the present invention comprises a combination of features and advantages which enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.